Fill a cocktail shaker with ice cubes.
Add the London Dry Gin, cranberry juice, lime juice, and simple syrup to the shaker.
Shake vigorously for 15 seconds until well-chilled.
Strain the mixture into a highball glass or chilled coupe filled with fresh ice.
Top the glass with tonic water and stir gently with a bar spoon.
Garnish with a sprig of rosemary, a few fresh cranberries, and an orange wheel to serve.